Stage 1
upto – 250 C – precipitation of eta-carbide, partial loss of tetragonality of martensite.
Steels above 0.25 wt% carbon precipitate hexagonal close-packed eta-carbide within the supersaturated martensite until 0.25 wt% carbon level is reached, martensite preserves some tetragonality. The orientation relationship between the laths or rodlets and the cube planes of the matrix was first described by Jack [1].

I don’t think it’s true that we will always get bainite during stage 2 tempering. The TTT diagram is for transformation from austenite, once transformed to martensite the starting microstructure will have an effect. It might be possible that some of these steels will form bainite, but I myself haven’t seen (but havent looked for!) the experimental evidence.

Looking for surface relief caused by the displacive transformation might be one thing to do, but this experiment should also probably be done in a dilatometer so that it is possible to distinguish bainite from any martensite that forms upon the cooling from the tempering temperature.